I'm using Joomla 3.7 - k2 2.7.1 and php 7.0
If I enable the native Joomla editor, the K2 content tab does not work. I have to use the JCE editor, but I prefer to use the native Joomla editor. See below for the problems.

See the video
www.youtube.com/watch?v=u3PSEAEVvtg&feature=youtu.be

Hello,

Can you try disabling all 3rd party K2 extensions to see if the issue is resolved?

I am not using any 3rd party extension.

Understand, the problem is in the editor of the page, in the content tab.

It's a bug from the Joomla native publisher, in this version Joomla 3.7

If I enable another editor works correctly.

You are using a tabs extension (I think at least from the video).
Is the native editor failing in the articles as well?